The invention relates to a method of securing an electric contact of a metal to a layer of a sintered thick-film paste, which is situated on an electrically insulating substrate.
The method mentioned above is used, inter alia, to manufacture thick-film resistors and heating elements comprising a resistance layer of a sintered thick-film paste. In the manufacture of such resistance elements, first, a resistance layer in the form of a thick-film paste is provided on an electrically insulating substrate, for example, by means of screen-printing. Subsequently, this layer is sintered at an elevated temperature so as to form a resistance layer of a sintered thick-film paste. After this sintering treatment, electric contacts, for example in the form of lugs or wires of metal, are secured to the sintered layer.
Customarily, such contacts are soldered directly onto the sintered layer, for example by means of a tinman's solder. However, the electrical and mechanical reliability of a metal wire secured in said manner is insufficient. For example, it has been found that the intermetallic bond between the metal contact and the sintered resistance layer is not as good as it should be. It has further been found that soldering the contact directly to the sintered layer may lead to fracture of the ceramic material owing to strong, local heating of the layer.
In accordance with another known method, wires are secured to the ceramic layer via an intermediate layer which is provided by vapor-deposition or sputtering. However, this method is relatively expensive.